The present invention relates to a stator of a single-phase electric motor with four salient poles arranged so that their axes are parallel and arranged in two pairs which are opposite with respect to the cylindrical cavity that contains the rotor, the pole shoe of each salient pole being inclined at an angle, with respect to the axis of the respective pole, so as to allow the pole shoes to form the cylindrical cavity for the rotor.
A conventional stator of a single-phase electric motor with four salient poles or the like usually has poles which are thicker than the yoke and are directed substantially radially, starting from the yoke whereto they are rigidly coupled, toward the inside of the stator. Each pole also has, at its end, a pole shoe. The four pole shoes surround the rotor without contact, i.e., they are arranged so that a cylindrical interspace (gap) is maintained between the pole shoes and the rotor. The thickness of the interspace can be constant or can be variously shaped according to the shape and arrangement of the pole shoes. Furthermore, the excitation winding is arranged around each one of the four poles and is constituted by an adapted number of turns of insulated conducting wire which, when electric current flows therethrough, induces in the stator an electromagnetic force that produces the rotation of the rotor.
It is also known that in so-called "shaded-pole" motors, the pole shoes are cut so as to form four auxiliary poles, around each of which a short-circuited winding is wound. The four auxiliary poles, together with the four windings, improve static torque at startup.
In practice, it has been found that in most cases the operation of winding the excitation windings around the four poles is highly onerous and that the material used is also considerable because it is not always distributed efficiently.
Some contrivances and/or modifications have been devised in order to reduce the amount of magnetic metal laminations used, to reduce the number of windings to just two and to simplify their assembly, but none of these contrivances has proved to be useful enough to be used in the vast majority of commercially available four-pole motors, much less in shaded-pole motors, which are used mainly in the field of fans in general and in the refrigeration industry and for power yields usually no higher than 50 W.